The present invention relates to a control system intended for use with robots, plant and industrial facilities, and more particularly to a feedback control device which uses a sensor for feedback control of the state of a controlled object.
FIG. 1 is a block diagram of a conventional feedback control system. In FIG. 1, a controlled object 1, which is a machine, an object, a robot, or industrial equipment, outputs a controlled quantity. A converting unit 2 converts the controlled quantity output from the controlled object 1 to a feedback quantity suitable for comparison with a desired value or command for the control system. A control unit 4 amplifies or converts the difference between the desired value and the feedback quantity, which is a control deviation, to an actuating signal suitable for controlling an actuating unit 3. The activating unit 3 converts the actuating signal from the control unit 4 to a manipulated variable or control input for controlling the object 1.
In FIG. 1, the feedback control is performed in accordance with the following procedure. First, a controlled quantity is detected by the detecting unit 2 and then converted to a feedback quantity. Next, a comparison is made between the desired value and the feedback quantity to obtain the control deviation. In response to the sign and magnitude of the control deviation, the control unit 4 applies to the actuating unit 3 such an actuating signal as to reduce the control deviation. The actuating unit 3 applies the control input corresponding to the actuating signal to the controlled object 1, whereby a corrective operation is performed.
In order to make the controlled quantity of the controlled object 1 equal the desired value, the feedback control system feeds back the controlled quantity detected by the converting unit 2 to compare it with the desired value, and automatically performs the corrective operation by the actuating unit 3. The feedback control can lessen the influence of not only a disturbance, i.e., a variation in the controlled quantity other than a variation in the desired value but also a variation in a parameter such as the amplification of an amplifier used in the control system and allows the controlled quantity to correspond to the desired value.
The feedback control system aims to bring the value of the controlled quantity closer to the desired value as quickly as possible. However, in a conventional control device, if its gain is low, then the controlled quantity will not approach the desired value easily and, consequently, will result in a slow response. The actuating signal output from the control unit 4 of FIG. 1 is not necessarily a proper value because the output of the controlled object is generally delayed against the input. If, therefore, the gain of the control device is increased for quick-response control, then the stability of control will be lost and the controlled quantity will thus diverge or oscillate.